It is conventional to fabricate a hose from a composition of “NBR PVC” corresponding to a mixture of acrylonitrile butadiene rubber and polyvinyl chloride. A hose of this composition is typically used for transporting automotive fuels such as gasoline having low permeability. Regulation of the permeability properties of hoses in view of global environmental protection is expected to be imposed in the future. Moreover, a growing demand for a highly permeable fluid such as hydrogen gas or carbon oxide gas for a fuel cell is expected to obsolete a hose composed solely of an organic material (e.g. rubber, resin).
A hose comprising a bellows metallic tube in theory should permeate no fluid and should therefor be suitable for transporting fluids of very high permeability. Accordingly, even when hydrogen gas is used for a fuel cell, the permeability to hydrogen gas of a bellows metallic tube is “0,” providing complete protection against leakage.
Hoses comprising a bellows metallic tube are known to the prior art as taught and described in Japanese patent publication No's: (1) Japanese Unexamined Patent (Kokai) No. 2001-182872; (2) U.S. Pat. No. 6,631,741; and (3) Japanese Unexamined Utility Model (Jikkai) No. S51-150511.
FIG. 3 is a diagram depicting one embodiment of a hose comprising a bellows metallic tube to be used herein as a comparative example in the explanation of the subject invention.
FIG. 3 shows a hose body 200 in cross section comprising a plurality of laminated layers with a bellows metallic tube 202 forming the innermost layer of the hose body; an elastic layer 204 laminated in a radial direction over the bellows metallic tube 202; a reinforcing layer 206 laminated over the elastic layer 204; and an outer layer 208 laminated over the reinforcing layer 206.
Inner layer 204 and outer layer 208 are both composed of an elastic material preferably of rubber.
Inner layer 204 is formed in such a manner that it fills the gaps formed in the valleys of the corrugated bellows portion 222 of the bellows metallic tube 202 as will be described later.
Reference Number 210 is a metallic sleeve externally mated to the longitudinal edge at one end of hose body 200. This is preferably accomplished by compressing the sleeve along the longitudinal edge of the hose body 200, against a rigid insert pipe 212 using, for example, a conventional crimping tool (not shown).
The metallic sleeve 210 compresses the longitudinal edge of the hose body 200 against the insert pipe 212 so that the compressed longitudinal edge is restricted from movement both inwardly and outwardly.
The bellows metallic tube 202 inner layer has a corrugated bellows portion 222 (“corrugated bellows portion”) and an integral non-corrugated straight tube portion 214 (“straight portion”) extending axially from the corrugated bellows portion 222. The straight portion 214 is externally mated to the insert pipe 212 upon crimping the sleeve 210.
The straight portion 214 has a section 216 (“extended section”) which extends outwardly from the hose body 200 in an axial direction. The metallic sleeve 210 includes a flange 218 which abuts the longitudinal edge of the hose body 200 and extends transverse to the axial direction into a groove 220 formed in the rigid insert pipe 212 so that upon crimping the sleeve 210 against the pipe 212, the straight portion 214 will deform within the groove 220 to prevent sliding of the straight portion 214 in an axial direction.
Note that the diameter of the straight portion 214 is essentially equal to the maximum outer diameter of the peaks 222a in the corrugated bellows portion 222 when contracted as is illustrated in FIG. 5(A).
In a bellows metallic tube of this type, the corrugated bellows portions 222 stretches in an axial direction upon internal pressurization as illustrated in FIG. 4 (B).
When pressurized, the pitch of the bellows portion expands in an axial direction as illustrated in FIG. 5 (A), with its peaks 222a shrinking and its valleys 222b expanding. In other words, the peaks 222a and the valleys 222b contract or expand to reach the mean diameter (the mean value of the diameters of the peaks 222a and the valleys 222b) of the bellows portion 222.
In contrast, the straight portion 214 does not deform in a radial direction when it is internally pressurized. The result of internal pressurization is plotted in FIG. 5 (B) wherein a step is generated between the straight portion 214 and the adjacent bellows portion 222, generating a large localized deformation or stress on the corrugated bellows portion 222, specifically at the location adjacent the straight portion 214. The same phenomenon is observed in pressurizing tests in which the hose is repeatedly pressurized internally. Disintegration occurs at a point of stress (particularly at the first and second peaks 222a or valleys 222b) derived from large local distortion and resulting exhaustion.
The above description relates to an embodiment in which the straight portion 214 corresponds to a restricted portion formed at the longitudinal edge of the bellows tube 202. It would also apply to a restricted portion formed in accordance with the following alternative arrangements:
(1) directly welding one end of the bellows portion 222 onto the insert pipe 212; or (2) forming an imperfect bellows at one end of the bellows portion 222 to be used in place of the straight portion 214 with the imperfect bellows having corrugations initially made larger than the corrugations of the bellows portion 222 while the differential diameter between peaks and valleys is made small. Any of the above alternatives would result in the same problem as long as it functions to form a restricted portion in the inner layer at the longitudinal edge of the bellows tube 202.
The above examples are described with reference to hoses for transporting hydrogen gas for use in fuel cells. These problems, however, are commonly observed in hose applications including (1) transporting a fuel (e.g. gasoline), where a hose is exposed to high temperature and high pressure (where low-gasoline permeability becomes a crucial issue) to protect air from gasoline contamination or to provide larger outputs from equipment; (2) transporting carbon dioxide in the form of a fluid, whose molecular weight is small, resulting in high permeability; and (3) other fields where gas permeability regulations are stringent.